A typical circuit board includes a section of circuit board material (e.g., fiberglass, copper, vias, etc.) and circuit board components attached or mounted to the section of circuit board material. Examples of circuit board components include integrated circuits (ICs), resistors, and inductors. Typically, these circuit board components generate heat during operation. A fan assembly typically generates an air stream that passes over the components to conducts the heat away from the components. The air stream removes the heat so that the components do not operate in an unsafe (e.g., relatively high) temperature range that causes the components to operate improperly (e.g., generate a signal incorrectly) or sustain damage (e.g., overheat, burnout, etc.).
Some ICs include heat sinks to facilitate cooling. In general, a heat sink is a flanged metallic device that attaches directly to the package of the IC. As the IC generates heat, heat flows from the IC package to the heat sink, and dissipates into the surrounding air. The air stream generated by the fan assembly then carries the heat away thus cooling the IC.
Conventional circuit boards utilize a relatively large number of components that encompass a given amount of surface area or real estate on a component side of the circuit board. As the number of components on the circuit board increase, the amount of real estate available for traces (e.g., electronic connections among the components) decreases. Certain circuit boards include relatively larger circuit board components, such as application specific integrated circuits (ASICs), located on a solder side of the circuit board, opposite to the primary, component side of the circuit board. By locating the circuit board components on the solder side of the circuit board, manufacturers increase the amount of surface area or real estate available for traces on the component side of the circuit board.
In order to cool the circuit board component when mounted to the solder side of the circuit board, heat sinks have been conventionally utilized. For example, one such conventional heat sink includes a receptacle that fastens to a support assembly where the support assembly attaches to and supports the circuit board. The heat sink also includes an adjustable member that engages the receptacle and is movable relative to the receptacle in order to control a distance between the adjustable member and the circuit board component. The heat sink can therefore be moved to a position (e.g., in full contact with a circuit board component package, into contact with thermal transfer material that contacts the circuit board component package, etc.) that allows the heat sink to transfer heat from the circuit board component to another structure, such as the support assembly. Such heat transfer allows cooling of the circuit board component during operation even when the component resides in a location having limited space.
Embodiments of the present invention improve upon the heat sinks of the prior art and provide mechanisms and techniques for cooling a circuit board component mounted to a circuit board. The heat sink of the present invention includes a device portion, a bend portion, and a support portion that thermally couples the circuit board component to a support member, thereby allowing for heat transfer from the circuit board component to the support member. The bend portion of the heat sink allows for displacement of the device portion relative to the support portion to limit the amount of stress generated by the heat sink on the circuit board component. The geometry of the heat sink further allows placement of the heat sink within the relatively narrow space conventionally formed between the circuit board and the support member.
In one embodiment, the invention relates to a heat sink assembly configured to cool a circuit board component mounted to a circuit board. The heat sink includes a device portion configured to thermally contact the circuit board component where the device portion defines a first plane. The heat sink further includes at least one support portion integrally formed with the device portion and in communication with a support member where the at least one support portion defines a second plane substantially parallel to the first plane defined by the device portion. The heat sink also includes a bend portion integrally formed between the device portion and the at least one support portion where the bend portion allows for displacement of the device portion relative to the at least one support portion and controls a stress generated by the device portion on the circuit board component when the support member couples to the circuit board.
The heat sink of the present invention improves over the heat sinks of the prior art in that the present heat sink is formed as a single component, rather than from multiple components. The use of a single component heat sink rather than a multiple component heat sink can reduce manufacturing costs. Furthermore, the geometry of the heat sink (e.g., the device portion, bend portion, and support portion) improves upon the heat sink of the prior art by limiting the amount of stress induced by the heat sink on the circuit board component, thereby limiting damage to the circuit board component caused by the heat sink.
In another embodiment, the heat sink assembly includes a loading portion located between the circuit board and the support member and contacting the at least one support portion. The loading portion generates a load on the support portion, thereby securing the support portion to a surface of the support member. The loading portion improves over the prior art by coupling the support portion of the heat sink to a surface of the support member by a compression force, rather than coupling the heat sink to the support member through holes formed in the support member. The loading portion eliminates the need for creating openings or holes within the support member to secure the heat sink to the support member, thereby reducing manufacturing costs.
In another embodiment, the heat sink assembly includes at least one retainer in communication with both the device portion and the circuit board component each retainer secures the device portion to the circuit board component. In certain cases, manufacturers use thermal adhesive between the circuit board component and the heat sink where the thermal adhesive has relatively high thermal transfer characteristics but relatively low adhesion characteristics. To limit the possibility of disassociation of the heat sink and circuit board component caused by failure of the adhesive the assembler uses the retainer to secure the device portion to the circuit board component.
In another embodiment, the heat sink assembly defines a width between the plane defined by the device portion and the plane defined by the at least one support portion where the width is substantially between a range of 0.55 mm to 2.05 mm. The width of the heat sink further allows placement of the heat sink within the relatively narrow space conventionally formed between the circuit board component and the support member.
In another embodiment, the bend portion of the heat sink defines a bend length where the bend length limiting plastic deformation of the heat sink when the support member couples to the circuit board. If the heat sink were to plastically or permanently deform, the loads generated between the device portion of the heat sink and the circuit board component could be reduced, thereby reducing thermal contact between the device portion and circuit board component. By limiting plastic deformation of the heat sink, the bend length maintains loads generated between the circuit board component and the device portion of the heat sink, thereby maintaining thermal contact between the component and the heat sink.
The features of the invention, as described above, may be employed in electronic equipment and methods such as those of Cisco Systems of San Jose, Calif.